1. Field of the Invention
This invention relates to an electronic fuel injecting method and device for an internal combustion engine, and more particularly to improvements in an electronic fuel injecting method and device for an internal combustion engine suitable for use in a motor vehicle engine having a group injection type electronic fuel injecting device and adapted to control fuel injection timings for each group in accordance with reference signals generated in the proximity of intake top dead center of a predetermined cylinder and angle signals generated at every predetermined rotary angles.
2. Description of the Prior Art
Heretofore, there has been adopted a method of using electronic fuel injecting device as one of the methods feeding a mixture of a predetermined air-fuel ratio to combustion chambers in an internal combustion engine such as a motor vehicle engine. Under this method, a plurality of injectors equal to the number of engine cylinders are provided on an intake manifold of the engine to inject fuel into the engine, and valve opening times of the injectors are controlled in accordance with the operating conditions of the engine, so that the mixture of a predetermined air-fuel ratio can be fed to the combustion chambers of the engine.
Three methods of controlling the fuel injection timings of the electronic fuel injecting device are generally known, including a so-called simultaneous injection method in which injectors for every cylinder open their valves all at once in synchronism with rotation of the engine, a so-called group injection method in which, for example, the injectors are divided into two groups and the injectors in each group open their valves all at once, and a so-called sequential injection method in which the injector for each cylinder sequentially opens its valve. Among those, the group injection method can effect fine and close control as compared with the simultaneous injection method, and further, control is simple as compared with the sequential injection method.
In the case of adopting this group injection method, it is a common practice that control is effected on the fuel injection timings for every groups in accordance with reference signals generated in the proximity of intake top dead center of a predetermined cylinder and angle signals generated at predetermined rotary angles, e.g., at every 180.degree.CA (crank angles) in the case of an in-line four cylinders engine. However, in the case of incorporating both a reference signal sensor and an angle signal sensor in a distributor as in the prior art, there occurs a driving region where, particularly, discrimination of the reference signals cannot be accurately carried out due to a magnetic interference between the reference signals and the angle signals, thereby resulting in an improper group injection.
More specifically, a crank angle sensor 8 incorporated in a prior art distrubutor, as shown in FIGS. 1 and 2, is constituted by: two rotors affixed in parallel to a distributor shaft 10, including a reference signal rotor 12 formed on the outer periphery thereof with a projection 12a for emitting reference signals generated in the proximity of intake top dead center of a predetermined cylinder and an angle signal rotor 14 formed on the outer periphery thereof with four projections 14a for emitting angle signals generated, at every predetermined rotary angles, for example, at every 180.degree.CA in the case of an in-line four cylinders engine; a reference signal pickup provided around the reference signal rotor 12, for obtaining reference signals from approaching conditions of the projection 12a; and an angle signal pickup 18 provided around the angle signal rotor 14, for obtaining angle signals from approaching conditions of the projections 14a.
For example, varying conditions of the reference signals and the angle signals obtained by the reference signal pickup 16 and the angle signal pickup 18 in the crank angle sensor 8 as described above are shown in FIG. 3. It is apparent from FIG. 3 that, particularly, noise signals owing to the angle signals are caused to the reference signals due to a magnetic interference therebetween. This condition of magnetic interference is variable in accordance with a rotational speed of the engine, and, for example, as shown in FIG. 4, both an output peak voltage level A of the reference signal and an interference noise peak voltage level B caused to the reference signal by the angle signals increase with the increase in the rotational speed of the engine. In consequence, for example, if a judging level Vth for the reference signal is set such that satisfactory reference signals can be obtained in a normal operating region ranging from 500 to 4000 rpm of the engine rotational speed as shown in FIG. 4, then, during a low rotational speed of less than 500 rpm of the engine rotational speed, the reference signal output peak voltage level A becomes lower than the judging level Vth, whereby the reference signal cannot be judged at all, while, during a high rotational speed of more than 4000 rpm of the engine rotational speed, the interference noise peak voltage level B exceeds the judging level Vth, so that the noises are misjudged as the reference signals.
In consequence, heretofore, it has not been able to accurately judge the reference signals during the low and high rotational speed operations of the engine and fuel injections have been performed at erroneous timings, thus possibly lowering the performance of the internal combustion engines.